Video conferencing typically involves video media transmitted in a certain format, such as an H.264 data stream, over a packet-based network. H.264 video streams comprise different types of frames, but not all frames include all of the data to be displayed at any given time. For instance, Inter-frames, or I-frames, are the only type of frame that is not coded with reference to any other frame; P-frames are coded predictively from a previous I-frame or P-frame; and B-frames are coded predictively from I-frames and P-frames.
In a switched video conferencing system, there are a variety of situations that require the sending of a Fast Video Update (FVU) message, also referred to as an inter-frame request, to accelerate the transmission of an I-frame from a video source. These situations are significantly different from those encountered in a traditional Multipoint Conferencing Unit (MCU). In an MCU that decodes the source video streams and then re-encodes a new stream to be sent to one or more destinations, packet loss or corruption only extends between the MCU and a single endpoint. Alternatively, in a voice-activated video switching system, the sending of an FVU by one or more destination endpoints may need to extend through the conferencing system and propagate all the way back to a source endpoint. This end-to-end propagation of FVUs can cause more FVUs to be sent to a source than necessary, which may result in bandwidth overruns or even congestive collapse of a source stream as unwanted FVUs cause the encoder to generate too many I-frames.